feat(tasks): SessionStart reads the claim — a compaction gets its work back (milestone 381 step 3)

The claim now pays rent to the session that set it. The SessionStart hook
sends the host's `source` and the session id; the server renders a claim
section by source (task_claims.render_claims):

- compact / clear: the work this session had claimed, each with its two
  latest log entries, so a compacted session resumes from the record
  rather than from a count of open tasks.
- startup / clear: other sessions' live claims (may still be running) and
  in-progress tasks whose claim went quiet (abandoned mid-task).
- fork: the same, framed as "two sessions may now hold this".
- resume, or no source sent: nothing.

The task sidebar shows a live claim as "Being worked" and a dead one on
open work as "Went quiet", so the operator sees a session die mid-task.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugin/hooks/scribe_session_context.sh

@@ -187,8 +187,14 @@ if [ -n "$url" ] && [ -n "$token" ] && command -v curl >/dev/null 2>&1; then
   marker_why=${marker_read#*$'\t'}
   repo=$(git -C "$repo_dir" remote get-url origin 2>/dev/null || true)
   scope=$(scribe_scope_query "$repo_dir")
-  q=""
-  [ -n "$scope" ] && q="?${scope}"
+  # The source and the session id decide what the claim section says
+  # (milestone 381): a compaction gets back the work this session had claimed,
+  # with its latest logs; a new session hears about other sessions' claims.
+  sid_now=$(scribe_json_pick "$event_flat" '.session_id')
+  q="source=$(printf '%s' "$source" | scribe_urlenc)"
+  [ -n "$sid_now" ] && q="${q}&session_id=$(printf '%s' "$sid_now" | scribe_urlenc)"
+  [ -n "$scope" ] && q="${q}&${scope}"
+  q="?${q}"
   # ONE FETCH, NAMED WHEN IT FAILS (#4366). This used to be `curl -f … ||
   # body=""`, which folded a timeout, an HTTP error and a refused key into one
   # sentence — so a session that started blind could not say why, and neither